1. Field of the Invention
The present invention relates to a polarizing beam splitter, and more particularly to a polarizing beam splitter and a polarizing beam splitter film. The polarizing beam splitter may be suitable for, for example, a light pickup optical system using a blue laser, a projection optical system, or the like.
2. Description of the Related Art
A light pickup optical system for a blue region requires a polarizing beam splitter having polarization separation characteristics such that a transmissivity of a polarized light p and a reflectivity of a polarized light s in a wavelength region of around 405 nm are both nearly 100%. Currently, however, the divergence angle of a blue laser is significant. Therefore, when an ordinary polarizing beam splitter film is used, the transmissivity of the polarized light p is largely decreased due to varying the angle of incidence.
Japanese Unexamined Patent Publication Nos. 08-146218 and 09-184916 disclose polarizing beam splitters having predetermined polarization separation characteristics with respect to even a broad angle region, where a divergence angle of incident light is ±5° or above. For example, a polarizing beam splitter film disclosed in No. 09-184916 includes a first stack constituting 0.8×λ/4≦H≦1×λ/4 and 0.7×λ/4≦L≦1×λ/4, and a second stack constituting 1.3×λ/4≦H≦1.5×λ/4 and 1.2×λ/4≦L≦1.5×λ/4, where λis central wavelength of a split light, H is an optical film thickness of a film made of a high-refractivity material, and L is an optical film thickness of a film made of a low-refractivity material.
However, in the case of the polarizing beam splitter films disclosed in No. 08-146218 and No. 9-184916, an angle dependency of the polarized light scan only be controlled at approximately 20% in terms of the transmissivity, which shows insufficient polarization separation characteristics. Thus, when the polarizing beam splitter film is used in a light pickup optical system using a blue laser, projection optical system, or the like, there is a problem of a decreased light quantity.